The present invention relates to a method and device for generating a decoded and synchronized output of m-bit pattern words from an input bit-stream comprising frames with corresponding n-bit pattern symbols as well as a n-bit comma symbol and in which bit-skip may have occurred, with m<n.
The invention further relates to a multi-beam lithography system comprising such a decoding device, and to a beam modulator array comprising such a decoding device.
Decoding of n-bit pattern symbols to m-bit pattern words, with m<n, is known, for instance from 8B/10B symbol mapping in which a number of consecutive 8-bit pattern words are mapped into a bit-stream of 10-bit encoded pattern symbols and vice versa. European Patent no EP 97 763 describes an implementation of 8B/10B mapping in which the redundancy provided by extending m bits to n bits is used to define at least one comma symbol which has a unique bit pattern that does not occur in any two consecutive symbol mappings for the pattern words. In this comma-based implementation, a number of m-bit patterns are encoded into a data frame which comprises a corresponding number of encoded n-bit symbols which map the m-bit pattern words, as well as a comma symbol to signify the start or end of the frame. A transmitter transmits the thus encoded data frames as a data stream to a receiver which decodes the received data stream by using decode-tables.
A drawback of this known implementation is that decoding of the data frame requires considerable amounts of logic, and thus space, at the decoder side, e.g. for hardwired lookup-tables and/or complex decode functions. If synchronization is to take place at the receiver as well then additional resources are required. Such resources are generally scarce at a decoder, in particular if the decoder is part of a beam modulator array of a multi-beam lithography system which is adapted for individually blanking beams of a plurality (e.g. tens of thousands, hundreds of thousands or more) of beamlets, as any space taken up by circuitries of the decoder cannot be used by modulators or the modulator array or by apertures in the beam modulator array for letting through the beamlets.
It is an object of the present invention to provide a method and decoding device which substantially overcomes this drawback. Further objects are to provide a multi-beam lithography system comprising such a decoder, as well as a beam modulator array comprising such a decoder.